How Does Passivation Work for Stainless Steel?

Passivation is one of the popular metal finishing processes that many parts use, including those made of stainless steel, tantalum, titanium, and others.

What Exactly is Passivation?

To understand what passivation is and how it works for stainless steel, it’s important to first take a closer look at how stainless steel functions. Stainless steel is naturally corrosion-resistant, but it can still experience corrosion over time.

Chromium is the element responsible for stainless steel’s corrosion-resistant nature, which forms a thin layer of chromium oxide that covers the steel when it encounters oxygen.

While this corrosion resistance is in place, it doesn’t necessarily make stainless steel entirely impervious to corrosion. In many cases, foreign substances such as materials from machine cutting tools and other equipment can gradually wear down the stainless steel over time.

Passivation is used to remove these contaminants and help retain the integrity of the original surface. You can then use an anodizing service to get the right color for your parts.

How Passivation Works

Passivation works by chemically removing free iron from the surface of stainless steel parts, forming a thin oxide layer that further improves the parts’ resistance to corrosion. The passivation process is ultimately effective for many types of parts at maximizing corrosion resistance, while at the same time increasing the longevity of those parts.

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Sometimes passivation will require sodium dichromate, which is added to the acidic baths to encourage faster formation of the oxide layer or film. However, the use of this element has significantly decreased since the use of citric acid and ultrasonics have become more ideal.

This is because both of the latter encourage oxygen formation at the surface of the material while it’s still immersed in the acid solution.

Keep in mind that passivation is used to simply improve upon the oxide layer of these parts, rather than completely restoring the part and making it completely resistant to wear over time.

Is Passivation or Anodizing Right for My Metal Parts?

Passivation’s chemical process is widely used, but there are other types of finishing techniques that might be better suited for certain parts, including those with stainless steel construction.

For instance, electropolishing is a process that has become increasingly popular over the years, and is commonly used to restore parts to their original condition by deburring parts through a process that removes just enough material from the surface to restore them.

It can be a challenge to determine which process is ideal for your parts, but you can always consult with metal finishing experts to decide on the most appropriate service.

Passivation continues to be a popular option for many different types of parts and circumstances, but metal finishing companies may recommend other alternatives depending on your part specifications and the specific needs for the application.

If your metal parts require finishing, passivation is still a great option in many cases, as one of the most effective means of improving parts’ corrosion resistance for many years.

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